Download A Dry Complex - Flinn Scientific

A Dry Complex
Transition Metal Complex Ions
SCIENTIFIC
Introduction
Show the formation and color of coordination compounds of copper with ammonia and water.
Concepts
• Transition metal complexes
• Reversible chemical reactions • Lewis acids and bases
Materials
Ammonia gas supply
Copper(II) sulfate, anhydrous, CuSO4, 30g
Copper(II) sulfate, pentahydrate, CuSO4z5H2O, 30g
Water
Beaker, 50-mL
Pipet, thin-stem
Stopper, solid, #2
Syringe with stopcock valve
Test tube holder
Test tube rack
Test tubes, 20 × 150 mm, 4
Safety Precautions
Ammonia is toxic and irritating or fatal by inhalation as well as a moderate fire risk. Use ammonia gas only under an operating fume
hood. Be aware of the hot test tubes and only use borosilicate glass test tubes. Be aware of the heat that can be generated by the addition
of water to anhydrous CuSO4. Wear chemical splash goggles, a chemical-resistant apron, and chemical-resistant gloves. Please review
current Material Safety Data Sheets for additional safety, handling, and disposal information.
Preparation
1. Fill two test tubes about 1⁄3 full with anhydrous CuSO4.
2. Fill two test tubes about 1⁄3 full with CuSO4 pentahydrate.
Procedure
1. Using a thin-stem pipet, add several drops of water using a thin stem pipet to the anhydrous CuSO4. Observe the
temperature and color changes in the test tube.
2. While under a fume hood, use a syringe with a stopcock valve to obtain some ammonia gas. Slowly add the gas to the
other test tube with anhydrous CuSO4. Stopper and gently shake the test tube. Observe the formation of the
tetraammine copper(II) ion at the top of the test tube. A second sample of ammonia gas may need to be added.
3. As a control, add several drops of water using a thin-stem pipet to the CuSO4 pentahydrate and observe the lack of
temperature and color change. Instead a solution is formed.
4. Add ammonia gas to the remaining test tube with CuSO4 pentahydrate. Observe how the top of the CuSO4 is a darker
blue than the bottom.
Disposal
Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures
governing the disposal of laboratory waste. Dispose of the excess copper(II) sulfate according to Flinn Suggested Disposal
Method #26a.
© 2016 Flinn Scientific, Inc. All Rights Reserved.
Publication No. 91746
061616
1
A Dry Complex continued
Tip
• If anhydrous copper(II) sulfate is not readily available, it may be prepared by following these steps:
1. Fill several 20 × 150 mm test tubes about 1⁄3 full of CuSO4z5H2O.
2. Hold the test tube at about a 45° angle and gently heat over a Bunsen burner to drive off the water. Be careful—
overheating will cause decomposition of the CuSO4.
3. Use a paper towel to wick off the water that may have formed in the upper portions of the test tube.
4. Loosely stopper with a #2 solid stopper and allow to cool.
Discussion
Normally the formation of the tetraammine copper(II) ion is done by adding aqueous ammonia to a water solution
containing the hexaaquo copper(II) ion. After an initial precipitation of Cu(OH)2(s) from the basic ammonia solution,
further addition of ammonia solution causes the solid to dissolve and the formation of the dark blue tetraammine copper(II) ion
(ammonia is a stronger ligand than water). The addition of ammonia gas to anhydrous CuSO4 shows that the formation of the
copper(II) ammonia complex ions, Cu(NH3)42+, formally known as tetraammine copper(II) +ions, can occur outside of a water
solution.
CuSO4(s) + NH3 → CuSO4(s)zxNH3 or Cu(NH3)42+
CuSO4(s) + H2O → CuSO4z5H2O
CuSO4z5H2O(s) + NH3 → CuSO4z5H2O(s) + CuSO4zxH2OzyNH3
CuSO4z5H2O(s) + H2O → Cu2+(aq) + SO42–(aq)
The reactions can also be used as an example of Lewis acid-base reaction. The Cu2+ serves as the Lewis acid and H2O and NH3
serve as Lewis bases.
Connecting to the National Standards
This laboratory activity relates to the following National Science Education Standards (1996):
Unifying Concepts and Processes: Grades K–12
Evidence, models, and explanation
Constancy, change, and measurement
Content Standards: Grades 9–12
Content Standard A: Science as Inquiry
Content Standard B: Physical Science, structure and properties of matter, chemical reactions, interactions of energy
and matter
Flinn Scientific—Teaching Chemistry™ eLearning Video Series
A video of the A Dry Complex activity, presented by Jesse Bernstein, is available in Transition Metal Complex Ions, part of the
Flinn Scientific—Teaching Chemistry eLearning Video Series.
Materials for A Dry Complex are available from Flinn Scientific, Inc.
Catalog No.
C0102
C0107
GP1005
AP1718
AP2224
GP6030
Description
Copper(II) Sulfate, Pentahydrate, 100 g
Copper(II) Sulfate, Anhydrous, 100 g
Beaker, 50 mL
Pipet, Thin-Stem, Pkg/20
Rubber Stopper, solid, #2, Pound
Test Tubes, 20 × 150 mm
Consult your Flinn Scientific Catalog/Reference Manual for current prices.
2
© 2016 Flinn Scientific, Inc. All Rights Reserved.